There are several reasons that have made wave energy converters more attractive since the beginning of the present decade. First, there are global warming issues—carbon dioxide emissions must be reduced in many industrialized countries due to ratification of the Kyoto Convention. Also, recent hurricane seasons have created growing concerns among some industrialized countries about climate change. Cuts in greenhouse gas emissions may ultimately be needed to stabilize atmospheric concentrations of the gases and avert serious climate disruptions. This reduction in greenhouse gases may require a global transition to renewable low carbon energy sources and improvements in energy efficiency.
Secondly, a dwindling supply of peak oil reserves and growing demand of oil by large nations such as China and India, in addition to growing political tensions in oil producing countries, have increased oil prices tremendously. In the Annual Energy Outlook 2006 (AEO2006) report, prepared by the U.S. Energy Information Administration (EIA) and incorporated herein by reference, it is estimated that, as new oil fields are brought into production worldwide, world oil prices may decline to $46.90 per barrel (2004 dollars) in 2014, and then rise to $56.97 in 2030. This means that during the expected period of maturity of wave technology (2006-2015) and consolidation of its market (up to 2025), the price of oil is projected to be near or above US$ 50 per barrel. This scenario makes the development of alternative energy technology very viable.
Others issues such as declining coal use, increased opposition to hydroelectric dams, increasing demand for renewable energy sources, and deregulation of energy markets may contribute to the development of alternative energy technology, and in particular, ocean and wave energy converters.
Even though wave energy technology development has been going on for a long time, there are major challenges that must be surpassed before this type of technology may be widely used. Among these challenges are:                Lowering capital costs        Maintenance requirements;        Generating power based on a diffuse and variable resource; and        Power quality        Survivability in a harsh environment.        
The motion of ocean waves has long been considered a major potential resource of both potential and kinetic energy. At the same time, wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction. Techniques for changing the random forces generated by waves into useful energy in an apparatus may be through one or more of the following power take-off systems, including pneumatic systems, hydraulic systems, piezoelectric systems, electrical systems, and mechanical systems.
The background (prior) art for the present invention in principally found in US Patent Class 60, sub-classes 495-507, Class 290/42-44, 52-54, 60, Class 417/330-334, International Patent Class F03B13/00-18. Of particular interest are the following prior art patent applications and patents, all of which are incorporated herein by reference: US2006/0028026; U.S. Ser. No. 884080; U.S. Pat. Nos. 3,894,241; 4,524,283; 6,933,624; 6,925,800; 6,857,266; 6,711,897; 6,269,636; 6,208,035; 5,359,229; 5,105,094; 4,661,716; 4,599,858; 4,319,454; DE4129180; CA2464184; CN1506574; DE20312348U; GB2037899; GB2008686; GB1515744; GB2064665; GB190908116; NL1016103C; U.S. Pat. Nos. 1,346,399; 3,259,361; 4,241,579; 3,974,652; 5,359,229; 4,389,843; WO0075506; WO 2005 038244; WO 00017519; WO 00065708; WO 03098033; WO 04094814, WO8100284A1, JP07229470A2, JP2005299556A2, JP58062380A2, JP58079675A2, U.S. Pat. Nos. 4,249,639, 3,567,953, 6,644,027, 5,929,531, 4,392,060, 4,627,240, 3,959,663, 3,777,494, US20050237775A1, and U.S. Pat. No. 4,108,578.
The majority of the technologies described in the aforementioned references present one or many of the following problems. Some Prior Art designs have many moving parts that may fail in the long run, requiring frequent maintenance and repair. Other embodiments would not survive harsh weather or high waves of the maritime environment. Many of prior art devices have open power take-off (PTO) systems where the PTO system is not contained in an enclosed structure and thus open to the elements and the harsh salt-water environment.
Still other systems have very high capital costs due to the construction in open sea of fixed seabed structures. Other systems have high maintenance costs due to use of ropes and/or pulleys and/or chains and/or springs that may fail in the long run. In addition, the power quality is low due to the lack of a control system to maintain power quality in a variable resource or the inability to accommodate the variety of wave heights and periods, which occur on an hourly and daily and seasonal basis. These Prior Art systems have no self-oriented capability to position themselves to absorb the maximum amount of energy from waves and thus optimize energy production, or to position to absorb the minimum amount of energy from waves during storm sea conditions.
In addition, the lack of control systems in the Prior Art limits the ability to vary power generation amount with the size of waves. Power output is limited to the installed capacity of a generator and its operational limits. Many systems use only one generator per power take-off (PTO) system. Once the generator fails the conversion of energy stops, and the entire system is “down” until a service crew may be dispatched. Conversion is limited to one generator and therefore to its operational limits.
In devices where the power take-off (PTO) system is enclosed in a hull-like structure, there is not a positive pressure control inside the tide hull (hermetic hulls) to prevent entry of seawater. Since all of the floating offshore devices have PTO systems that interact with waves, they are exposed to infiltration through the areas where the actuating member meets the frame (or hull) underwater for long periods of times. Since one of the major purposes of design is to lower maintenance costs (months or years unattended in offshore location), control of leakage/infiltration is important.
In the case of electric power generation, some of the aforementioned Prior Art references confront the power quality in a variable resource (waves of variable significant wave height and wave periods) by maintaining constant speed of the main shaft through mechanical brakes and or increasing the load of the generators (electromagnetic braking); however all of those systems have limitations in the large range of waves of variable significant wave height and wave periods. Some others maintain constant speed of the generators by controlling hydraulic or airflow to the power take-off system.
In the International Patent Application WO8100284A1, incorporated herein by reference, it is mentioned in page 2, lines 12 to 16 “In the invention disclosed and described herein, each rack and pinion drive assembly mounted along the rotatable shaft provides a completely independent power stroke to the drive shaft regardless of what any of the other drive assemblies are doing . . . ” This means that all drive assemblies, or one, or any number of them can be transmitting power (engaged) to the drive shaft at any time. In our invention only one set of dual same diameter pinions can be engaged to the main rotary shaft at any time. Related to the completely independent power stroke by each rack and pinion drive assembly as mentioned above, WO8100284A1 mentions in page 8, lines 25 to 32: “One driving assembly 14 may be moved upwardly a short distance by a low wave while another may continue upward for a longer distance by a higher wave, and yet both will continue to apply driving force to rotary shaft 2 in the same direction of rotation without one driving assembly 14 working against or opposing another. The same is true on the downward stroke.” This is highly unlikely to occur in seas, lakes or ocean where waves rise and fall in random, unpredictable fashion. It would only occur if the upwardly (or downwardly) velocity of the float hit by the low wave is exactly the same upwardly (or downwardly) velocity of the float hit by the higher wave. It is highly more probable that the upwardly (or downwardly) velocity of the float hit by the higher wave will be greater than the upwardly (or downwardly) velocity of the float hit by the low wave. This would make the rotational speed transmitted to the drive shaft by the float hit by the higher wave greater than that transmitted by the float hit by the low wave, rendering the energy generated by the float hit by the low wave useless (i.e., this energy would not be transmitted to the drive shaft). This situation is avoided in our invention since all energy generated by the float at any time is transmitted to the main rotary shaft through a single set of dual same diameter pinions. The invention described in WO8100284A1 has a float attached to each independent rack and pinion drive assembly. Since the energy that is transmitted to the drive shaft is ultimately generated from the floats in contact with the waves, at a given wave high, the maximum amount of energy of this device will be generated if all float have the same upwardly (or downwardly) velocity at the same time. As mentioned above, this is highly unlikely. Therefore, it is probable that the energy generated by this device will be always lower than that possibly generated by its total floating capacity. In our invention, since there is only one float (large by design since all the power take off system including flywheels and generators are within it) all the floating capacity of our invention is used to generate energy at any time. The invention described in WO8100284A1 does not have a self-orienting capability. So, except in those locations where the waves will always come from the same direction, the device sometimes would be hit by waves in a perpendicular manner making floats to raise one after the other (and therefore lowering its energy absorption capacity), and sometimes would be hit by waves in a parallel manner making floats to raise all together. Sometimes it will be hit by waves in an angle. Our invention has a self-orienting capability. All the time when waves are within design parameters of the power take off system, our invention will orient itself in a parallel manner to the waves for maximum energy extraction per wave crest. When these design parameters are being surpassed, it will orient itself in a perpendicular manner to the waves for minimum energy extraction per wave crest. The invention described in WO8100284A1 does not have a submerging capability to deal with storm conditions. Ours does.
In the background of the International Patent Application WO2005069824, incorporated herein by reference, it is mentioned that in order to increase the efficiency of converting wave energy to electric energy using wave energy converters (WECs), “It has also been proposed to adjust the mechanical properties of the WEC to take into account the predominant wave frequency over a period of time. Incorporating such a proposal requires mechanical devices that change the spring, mass and damping of the WEC. However, to effectuate the called for proposed adjustments to the mechanical properties of a WEC is problematic since there is no practical way to provide continuous, or multiple level, tuning of the system”. In the same International Patent Application it is mentioned, “In all of known proposed wave energy converter efficiency-boosting schemes, the energy storage and/or tuning components are large and/or expensive making it difficult and/or expensive to produce commercially viable products.”
The aforementioned problems or challenges are precisely those which the present invention is oriented to solve.